Doctoral Dissertations

Date of Award

6-1970

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

K. M. Barth

Committee Members

S. A. Griffin, S. L. Hansard, J. K. Bletner, C. S. Hobbs, J. T. Smith

Abstract

Two experiments with fat- and lean-type growing pigs were conducted to measure differences in apparent nutrient digestibilities, nitrogen (N) retention, average daily gain, feed efficiency, protein efficiency and carcass composition and to examine relationships between N-retention data measured at three stages of growth and final carcass measurements. In experiment 1, 6 fat- and 6 lean-type barrows, weighing approximately 27 kg, were visually selected and randomly assigned in a 2 X 2 X 3 factorial arrangement to either high (18-16%) or low (14-12%) protein rations. Total-collection digestion and N-metabolism trials were conducted at 41, 70 and 95 kg of body weight. In experiment 2, 6 fat- and 6 lean-type barrows, initially weighing approximately 26 kg, were fed high-protein rations (20-16% crude protein). Total-collection digestion and N-metabolism trials were conducted at 31, 53 and 91 kg of body weight. No differences in the average daily gain was found between pig type. Lean-type pigs required significantly (P<.05) less feed intake to produce a unit gain in body weight and significantly less protein intake to produce a unit increase in the protein content of the edible carcass. Pig type appeared to have no effect on digestibility of dry matter, gross energy or crude protein (CP). Nutrient digestibility improved slightly as animals became older. Apparent CP digestibility of the high protein rations tended to be higher in experiment 1. Overall, lean-type pigs fed the high protein levels retained more N daily than fat-type pigs. However, during the first trial (30-40 kg body weight), fat- and lean-type pigs retained similar amounts of N daily (19.5 and 19.7 g, respectively). Lean-type pigs continued to retain the same amount at 60 kg of body weight. However, at 90 kg of body weight, daily N-retention decreased to 14.2 g. In contrast, fat-type pigs retained progressively less N per day as body weight increased (19.5, 14.3 and 10.4 g/day at body weights of approximately 35, 60 and 90 kg, respectively). In experiment 1, lean-type pigs fed the high-protein rations had greater amounts of ham, loin and shoulder and less backfat than leantype pigs fed the low-protein rations, indicating that the low level of protein was too low for maximum carcass leanness. In fat-type pigs, no improvement in carcass leanness was noted when the higher protein rations were fed, suggesting that with fat-type pigs the low protein rations were sufficient for maximum leanness. In experiment 2, lean-type pigs had significantly (P<.05) more length, higher percentages of ham, loin and shoulder, and less backfat than fat-type pigs. No differences were found in the weight of skin between the two types, but lean-type pigs had significantly (P<.05) more bone. Moisture and crude protein (either percent or amount) in the edible portion of the carcass was significantly (P<.05) greater in lean-type pigs, while ether extract was significantly lower. With high-protein levels, coefficients of correlation between daily N-retention data at each body weight and final carcass measure-ments improved as animals became older in both experiments. Coefficients of simple regression (and their standard errors) between daily N-retention data at each weight and final carcass measurements indicated that the standard error was too high for reliable carcass composition prediction from N-retention measured in the live animal.

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